.box {
    width: 400px;
    margin: 100px auto;
    position: relative;
}

.box .rocket {
    position: relative;
    animation: rocket-move 0.5s linear 0s infinite alternate;
}
.line1 {
    width: 2px;
    height: 166px;
    background-color: blue;
    position: absolute;
    top: 300px;
    left: 800px;
    transform: rotate(45deg);
    animation: yd 1s linear 0s infinite;
    opacity: 0;
}
.line2 {
    width: 2px;
    height: 266px;
    background-color: blue;
    position: absolute;
    top: 340px;
    left: 850px;
    transform: rotate(45deg);
    animation: yd 1s linear .4s infinite;
    opacity: 0;
}
.line3 {
    width: 2px;
    height: 266px;
    background-color: blue;
    position: absolute;
    top: 390px;
    left: 890px;
    transform: rotate(45deg);
    animation: yd 1s linear .68s infinite;
    opacity: 0;
}
.line4 {
    width: 2px;
    height: 266px;
    background-color: blue;
    position: absolute;
    top: 390px;
    left: 920px;
    transform: rotate(45deg);
    animation: yd 1s linear .2s infinite;
    opacity: 0;
}
@keyframes yd {
    0% {
        transform: rotate(45deg) translateY(-300px);
        opacity: 0;
    }
    50% {
        opacity: 1;
    }
    100% {
        transform: rotate(45deg) translateY(300px);
        opacity: 0;
    }
}
